XCOM 2 isn't out until next year, after its original November release was pushed back. Sad times, I know. Here to help you get through it is this video from "Firaxicon", where the game's developers had the opportunity to talk about XCOM 2's design "pillars".
The presentation consisted of four Firaxis employees, including creative director Jake Solomon, art director Greg Foertsch, leader producer Gareth DeAngelis and lead engineer Ryan McFall. FYI, you'll want to jump to the seven-minute mark to get to the talk itself.
Solomon drives the event to begin with and one of the first topics he covers is how the team wanted to expand on XCOM's design pillars. You have the tactics and strategy bits, but the developers wanted a third -- replayability, in the form of procedural maps:
We started to think about "What are the pillars of XCOM?" No matter what the setting is, at Firaxis, our games are built on mechanics. We don't come up with a story and say "Hey, now let's make a game to fit that." Instead we say "Whatever the story is, it has to fit the core mechanics of what the experience is."
In XCOM, those pillars are pretty clear. Obviously, you have the idea of tactical and strategy -- you have this tense tactical combat, where the stakes are high and then you have the strategic game that allows the player to expand and grow their forces. We added a new design pillar -- after Enemy Unknown, one thing we wanted to expand on was the idea of replayability.
The next part of the presentation covers how the maps are constructed and the difficulties faced when trying to generate areas that not only look good, but allow for interesting player decisions.
Beyond that you might not want to keep watching, depending on how spoiler-sensitive you are. While nothing of particular note is revealed, you do see some still images of new enemies. No real details, but you've been warned.